What Is Acute Mountain Sickness?

Acute Mountain Sickness, commonly shortened to AMS, is the body’s response to the lower oxygen levels found at high altitude. As you climb, air pressure drops, which means each breath delivers less oxygen to your bloodstream than it would at sea level. Your body is remarkably good at adapting to this — breathing rate increases, heart rate rises, and over a period of days your body produces additional red blood cells to carry oxygen more efficiently. AMS develops when someone ascends faster than their body can adjust to these changes.

Importantly, AMS is not a sign of weakness or poor fitness. It can affect seasoned mountaineers and first-time trekkers alike, and physical fitness offers little protection against it. What does help is a sensible, gradual ascent profile — which is exactly how Himalayan Unique Travels designs every high-altitude itinerary.

The Three Levels of AMS

AMS is generally described in three stages of severity, and recognising which stage you are in determines the right response.

Mild AMS: Symptoms are uncomfortable but manageable. Rest at the same altitude, and most people recover within a day without needing to descend.

Moderate AMS: Symptoms are more pronounced and need close monitoring, since this stage can progress to something more serious if ignored.

Severe AMS: This is a medical emergency. Immediate descent is required, regardless of the time of day or weather conditions.

Recognising the Symptoms

Mild AMS

Mild AMS feels similar to a bad hangover — a persistent, throbbing headache, mild nausea, fatigue, and a general sense of being unwell. Sleep is often light and broken, and appetite may drop. Standard headache remedies and rest at the same altitude usually resolve these symptoms within hours to a day.

Moderate AMS

At this stage, the headache no longer responds well to pain relief, nausea may progress to vomiting, and you may notice breathlessness even while resting. This requires closer attention from your guide and, in many cases, a precautionary pause in ascent until symptoms clear.

Severe AMS — HACE and HAPE

Severe AMS takes one of two life-threatening forms, and immediate descent is the only appropriate response to either.

HACE (High Altitude Cerebral Edema)

HACE involves swelling of the brain and is identified by a decline in coordination and mental clarity, on top of a severe headache that does not respond to medication. A simple field test our guides use is asking the affected person to walk heel-to-toe along a straight line; clear difficulty doing this (known as ataxia) is treated as a strong warning sign. Other indicators include confusion, unusual irritability, difficulty with simple tasks like packing a bag, and increasing drowsiness.

HAPE (High Altitude Pulmonary Edema)

HAPE is a build-up of fluid in the lungs and can develop with or without preceding AMS symptoms. Early signs include unusual fatigue, reduced exercise tolerance, and a dry cough. As it progresses, breathlessness occurs even at rest, the cough may bring up frothy or blood-tinged fluid, and lips or fingernails may take on a bluish tinge due to low blood oxygen. HAPE can develop within a couple of hours or build gradually over a few days, and it is often most likely on the second night after arriving at a new altitude.

How We Help Prevent AMS

Acclimatisation Built Into Every Itinerary

The single most effective protection against AMS is a gradual ascent, and this is built into the structure of every Himalayan Unique Travels trek. Our itineraries include planned rest days and sensible daily elevation gains rather than rushing to cover ground quickly. We strongly discourage shortening an itinerary purely to save time or money — doing so increases the risk of altitude illness and, in the worst case, an unplanned early descent that wastes both the trip and the cost of it.

Walking at a Sensible Pace

On trek, the aim is never to be first to the pass — it is to acclimatise safely and enjoy the journey. Younger, fitter trekkers are statistically more likely to develop AMS, often because they push the pace faster than their bodies are ready for. Walking at your guide’s pace, regardless of how strong you feel, gives your body the best chance to adjust.

Staying Fuelled and Hydrated

Fatigue and dehydration both worsen AMS symptoms. Eating well, even when appetite drops, and drinking fluids consistently throughout the day — roughly an extra litre for every hour of significant physical effort — both support your body’s natural acclimatisation process.

What to Avoid at Altitude

• Alcohol, which can suppress breathing and worsen oxygen levels overnight
• Sleeping tablets or tranquilisers, for the same reason
• Skipping meals, even if your appetite is reduced
• Ignoring early symptoms in the hope that they will pass on their own

Other Altitude-Related Risks We Prepare For

Cold, wind, and reduced circulation at altitude can also lead to frostbite on exposed fingers, toes, and ears, while intense high-altitude sun increases the risk of sunburn and snow blindness. Warm, layered clothing, proper eyewear, and high-SPF sun protection — all included on our packing list — address these risks directly.

How AMS Is Treated

Mild AMS

Rest at the same altitude (or a slightly lower one) until symptoms ease, which is typically a matter of hours to a day or two. Standard pain relief can help with the headache. If symptoms do not improve, descending to a lower elevation is the next step.

Moderate to Severe AMS

Our guides are trained to manage moderate AMS with descent, supplemental oxygen where available, and medication such as Acetazolamide (Diamox) under appropriate guidance. A portable hyperbaric (Gamow) bag may also be used to simulate lower altitude until the affected trekker can be moved down safely.

If HACE or HAPE Develops

Both conditions require immediate descent — ideally 1,000 metres or more — along with oxygen and, where needed, extended use of a hyperbaric bag while evacuation is arranged. This is precisely why Himalayan Unique Travels equips every high-altitude trek with trained guides, communication equipment, and a clear evacuation protocol with our Thimphu office.

Our Commitment to Your Safety

Every guide leading a Himalayan Unique Travels trek receives ongoing training in AMS recognition and emergency first aid. We would always rather adjust a schedule, add a rest day, or turn a group back than risk a guest’s health for the sake of an itinerary. If you have any questions about altitude, fitness, or medication such as Diamox before you travel, our team is happy to talk it through with you directly.